ABS molding compositions have been used over many years in large amounts for the production of all types of molded parts. The property spectrum of these thermoplastic resins ranges from relatively brittle to extremely tough.
A special area of use of ABS molding compositions is the production of molded parts that have to meet stringent requirements as regards impact toughness as well as the possibility of targeted adjustment (gradations between glossy and matte) of the surface gloss, for example in the automobile sector or for the production of housing parts.
ABS products with high toughness values and relatively high surface gloss may be produced using conventional ABS and employing large amounts of rubber; this is associated however with disadvantages as regards other properties, for example modulus of elasticity, heat stability and thermoplastic flowability.
ABS products with relatively low surface gloss can be obtained for example by solution polymerization or bulk polymerization processes; however products with high low-temperature strengths are not obtained by these processes.
Although it is true that certain improvements may be achieved by mixing conventional emulsion-ABS types with solution-ABS or bulk-ABS types (see for example U.S. Pat. No. 4,430,478), the stringent requirements as regards toughness and flowability while at the same time preserving the low surface gloss that is characteristic of bulk-ABS are however not met by these materials.
It is also known to mix ABS polymers produced by bulk polymerization with various graft rubber polymers having small and large particle sizes produced by emulsion polymerization (see for example U.S. Pat. No. 4,430,478, U.S. Pat. No. 4,713,420, EP-A 190 884, EP-A 390 781, EP-A 436 381 and the literature cited therein), though the resulting products do not have an improved toughness at low-temperatures.
EP-A 845 497 describes a mixture of ABS polymer obtained by bulk or suspension polymerization and a special graft rubber obtained by emulsion polymerization using two rubber components. The toughness of the molding compositions produced therefrom is however often not sufficient for the production of molded parts subjected to extreme stresses.
All these ABS polymers have, apart from the aforementioned mechanical disadvantages, a non-optimal pigmentability on account of the excessively high opacity and insufficient inherent color, as a result of which increased amounts of pigments are required to pigment the molding compositions and in addition the toughness is thereby negatively affected.
It has now been found that by a combination of at least two graft rubbers specially produced by emulsion polymerization with at least one graft polymer produced by solution, bulk or suspension polymerization, products can be obtained having a combination of very good toughness, good processability, adjustable surface gloss, good inherent color and reduced opacity.